Pre-distortion Multi-carrier Mobile Communication System

Orthogonal Frequency Division Multiplexing (OFDM) is one of the promising techniques for future wireless communication systems, since it is with high spectrum efficiency and robustness to the frequency selective fading environments. Orthogonal Frequency Division Multiple Access (OFDMA) is an efficient multiple access scheme based on OFDM with high bandwidth efficiency, which is suit for multi-user concurrent communication. However, OFDM and OFDMA are both multi-carrier systems and have the drawback of high peak-to-average power ratio (PAPR). In this case, when OFDM signals with high peak values pass through an amplifier, nonlinear distortions will be introduced so as to degrade the transmission performance. Distortion techniques own the advantagesin the following area, such as high capability of PAPR reduction, low redundance, flexible applications. They are the most widely applied techniques in PAPR reduction area. This dissertation mainly focuses on the distortion techniquesto reduce PAPR in OFDM/OFDMA systems.Firstly, the dissertation introduces the basic theory of OFDM/OFDMA techniques, the advantages and disadvantages as the background and theory basis.Secondly, the dissertation makes a theoretical analysis and mathematic calculation on the PAPR of OFDM signals, and clarifies the definition, the distribution and the models of PAPR, mainly focus on the comparison among current distortion techniques in PAPR reduction, so as to make a theoretical base for the latter sections.Windowing can effectively solve the out-of-band radiation problem from the conventional distortion techniques. Therefore, in the third part of this dissertation, we make theoretical analysis and simulation on windowing. But windwowing will introduce more in-band distortion, aiming at this problem, we propose a signal recovery method of windowing OFDM system, which is rebuilding windowing noise at the receiver to recover the transmitting data. This method can improve system's BER performance effectively.As one of the distortion methods, conventional repeated clipping and filtering method is widely applied for PAPR reduction. However, it owns the drawback of lower rate of convergence. In the fourth part of this dissertation, an improved method with more PAPR reduction is proposed, which is dividing OFDM signals into odd and even parts to make clipping respectively. The new method can achieve better PAPR reduction performance on the same number of iterations and complexity as traditional method.Finally, the dissertation investigates the PAPR reduction techniques under OFDMA system. We compare the PAPR of OFDMA signals with different sub-carrier allocation styles, analyze the method of in-band noise filtering and propose a low complexity PAPR reduction method for sequence interleaved OFDMA.